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Abstract:

A pneumatic artificial muscle (PAM) actuator body can be formed from an
elastic material that includes an inflatable chamber and a restraining
component, such as flexible, but inextensible fibers, that causes the
actuator to contract when the chamber is inflated with fluid (e.g., air
or water). The actuator body can be cylindrical or flat. The actuator
body can include a sensor layer formed of an elastic material including a
microchannel filled with a conductive fluid to sense the expansion of the
actuator body. The sensor layer can be configured to expand when the
actuator body is inflated causing the electrical resistance of the
conductive fluid to change. A sensor layer between the actuator body and
restraining component can be used to measure changes in the contraction
force of the actuator and a sensor layer outside of the restraining
component can be used to measure changes in the length of the actuator.

Claims:

1. A pneumatic actuator formed of an elastic material, the pneumatic
actuator comprising: a chamber extending along an axis from a first end
to a second end; an inlet connected to the chamber to enable a fluid to
be injected into the chamber; a plurality of flexible fibers coupled to
the first end and the second end; a first sensor layer extending along
the axis from the first end to the second end and coupled to the
actuator, whereby when a fluid is injected into the chamber causing the
chamber to expand, the first sensor layer is caused to expand; and
wherein the first sensor layer includes a first microchannel containing a
conductive liquid extending along a portion of the actuator whereby
expansion of the first sensor layer causes a change in at least one
dimension of the first microchannel and a change in electrical resistance
of the conductive liquid in the first microchannel.

3. The pneumatic actuator according to claim 2 wherein the first sensor
layer forms a cylinder that encircles the chamber and the plurality of
fibers forms a cylinder that encircles the first sensor layer and further
comprising a second sensor layer formed in a cylinder that encircles the
plurality of fibers; wherein the second sensor layer includes a second
microchannel containing a conductive liquid extending along a portion of
the actuator whereby expansion of the second sensor layer causes a change
in at least one dimension of the second micro channel and a change in
electrical resistance of the conductive liquid in the second
microchannel.

4. The pneumatic actuator according to claim 1 wherein the elastic
material forms a substantially flat body having a first side and second
side.

5. The pneumatic actuator according to claim 4 wherein the plurality of
fibers forms part of a fiber layer bonded to the first side of the flat
body.

6. The pneumatic actuator according to claim 5 wherein the first sensor
layer forms a layer that is bonded to the fiber layer that is bonded to
the first side of the flat body.

7. The pneumatic actuator according to claim 4 wherein the first sensor
layer forms a layer that is bonded to the second side of the flat body.

8. The pneumatic actuator according to claim 7 wherein the plurality of
fibers forms part of a fiber layer forms a layer that is bonded to the
first sensor layer that is bonded to the second side of the flat body.

9. The pneumatic actuator according to claim 8 further comprising a
second fiber layer, including a plurality of flexible fibers coupled to
the first end and the second end, bonded to the first side of the flat
body; and a second sensor layer bonded to the second fiber layer, whereby
when a fluid is injected into the chamber causing the chamber to expand,
the second sensor layer is caused to expand; and wherein the second
sensor layer includes a second microchannel containing a conductive
liquid extending along a portion of the actuator whereby expansion of the
second sensor layer causes a change in at least one dimension of the
second micro channel and a change in electrical resistance of the
conductive liquid in the second microchannel.

10. A pneumatic actuator formed of an elastic material, the pneumatic
actuator comprising: a first layer forming a chamber extending along an
axis from a first end to a second end; an inlet connected to the chamber
to enable a fluid to be injected into the chamber; a second layer
including a plurality of flexible fibers coupled to the first end and the
second end; a first sensor layer extending along the axis from the first
end to the second end and coupled to the actuator, whereby when a fluid
is injected into the chamber causing the chamber to expand, the first
sensor layer is caused to expand; and wherein the first sensor layer
includes a first microchannel containing a conductive liquid extending
along a portion of the actuator whereby expansion of the first sensor
layer causes a change in at least one dimension of the first microchannel
and a change in electrical resistance of the conductive liquid in the
first microchannel.

11. The pneumatic actuator according to claim 10 wherein the first layer
is formed from a substantially planar elastic material and the first
sensor layer is formed from a substantially planar elastic material.

12. The pneumatic actuator according to claim 10 wherein the first layer
includes a first side and a second side and the second layer is bonded to
the first side of the first layer and the first sensor layer is bonded to
the second side of the first layer, and wherein the pneumatic actuator
further includes a second sensor layer bonded to the second layer, the
second sensor layer extending along the axis from the first end to the
second end and coupled to the actuator, whereby when a fluid is injected
into the chamber causing the chamber to expand, the second sensor layer
is caused to expand; and wherein the second sensor layer includes a
second microchannel containing a conductive liquid extending along a
portion of the actuator whereby expansion of the second sensor layer
causes a change in at least one dimension of the second microchannel and
a change in electrical resistance of the conductive liquid in the second
microchannel; and a third layer bonded to the first sensor layer, the
third layer including a plurality of flexible fibers coupled to the first
end and the second end.

13. A method of making a pneumatic actuator comprising molding a first
layer of an elastic material, the first layer having a first surface;
applying a release material in a predefined pattern on the first surface
to define a fluid chamber; bonding a second layer of an elastic material
to the first surface containing the release material, whereby the second
layer bonds to the first surface except in an area of the first surface
where the release material was applied; bonding a first sensor layer to
the second layer, the first sensor layer including a first microchannel
containing a conductive liquid extending along a portion of the actuator
whereby expansion of the first sensor layer causes a change in at least
one dimension of the first microchannel and a change in electrical
resistance of the conductive liquid in the first microchannel.

14. The method according to claim 13 further comprising positioning a
negative mask on the first surface of the first layer and applying the
release material over the negative mask.

15. The method according to claim 13 wherein bonding the second layer of
elastic material includes molding the second layer of elastic material on
the first surface of the first layer.

16. A method of making a pneumatic actuator comprising molding a first
layer of an elastic material, the first layer having a first surface;
applying a release material in a predefined pattern on the first surface
to define a fluid chamber extending along an axis from a first end to a
second end; bonding a second layer of an elastic material to the first
surface containing the release material, whereby the second layer bonds
to the first surface except in an area of the first surface where the
release material was applied; bonding a third layer to the second layer,
the third layer including a plurality of flexible fibers extending along
the axis from the first end to the second end.

17. The method according to claim 16 further comprising positioning a
negative mask on the first surface of the first layer and applying the
release material over the negative mask.

18. The method according to claim 16 wherein bonding the second layer of
elastic material includes molding the second layer of elastic material on
the first surface of the first layer.

19. A method of making a pneumatic actuator comprising forming a first
layer of an elastic material, the first layer having a first surface;
applying a layer liquid elastomer in a predefined pattern on the first
surface to define a fluid chamber; bonding a second layer of the liquid
elastic material on the first surface containing, whereby the second
layer bonds to the first surface in the area where the liquid elastomer
was applied; bonding a first sensor layer to the second layer, the first
sensor layer including a first microchannel containing a conductive
liquid extending along a portion of the actuator whereby expansion of the
first sensor layer causes a change in at least one dimension of the first
microchannel and a change in electrical resistance of the conductive
liquid in the first microchannel.

20. The method according to claim 19 further comprising positioning a
mask on the first surface of the first layer and applying the layer of
liquid elastomer over the mask.

21. The method according to claim 19 wherein bonding the second layer of
elastic material includes bonding a layer of cured elastic material to
the layer of liquid elastomer on the first surface of the first layer.

22. A method of making a pneumatic actuator comprising forming a first
layer of an elastic material, the first layer having a first surface;
applying a layer liquid elastomer in a predefined pattern on the first
surface to define a fluid chamber; bonding a second layer of the liquid
elastic material on the first surface containing, whereby the second
layer bonds to the first surface in the area where the liquid elastomer
was applied; bonding a third layer to the second layer, the third layer
including a plurality of flexible fibers extending along the axis from
the first end to the second end.

23. The method according to claim 22 further comprising positioning a
mask on the first surface of the first layer and applying the layer of
liquid elastomer over the mask.

24. The method according to claim 22 wherein bonding the second layer of
elastic material includes bonding a layer of cured elastic material to
the layer of liquid elastomer on the first surface of the first layer.

25. A method of making a pneumatic actuator comprising: forming a base
layer having an embedded microchannel; positioning the base layer in a
mold; molding the base layer into the pneumatic actuator by adding liquid
elastomer into the mold and allowing the liquid elastomer to cure.

26. The method of making a pneumatic actuator according to claim 25
wherein the base layer is formed by molding a low friction fiber into the
base layer, allowing the base layer to cure, and removing the low
friction fiber from the cured base layer.

27. The method of making a pneumatic actuator according to claim 26
further comprising a mold wherein the mold is circular and includes an
inner post.

28. The method of making a pneumatic actuator according to claim 25
further comprising positioning flexible fibers in the mold prior to
adding the liquid elastomer.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit under 35 U.S.C. § 119(e) of
the U.S. Provisional Application No. 61/754,681, filed Jan. 21, 2013, the
contents of which are incorporated herein by reference in their entirety.

[0006] The present invention is directed to pneumatic artificial muscle
actuators including embedded sensors that enable control of the actuators
in real time.

[0007] 2. Description of the Prior Art

[0008] Pneumatic artificial muscle (PAM) actuators are used to provide
mechanical actuation in various fields, such as, robotics. The actuator
typically includes a cylindrical tube extending along an axis, sealed at
both ends, formed from an elastic material, such as rubber or silicon. A
pneumatic inlet is provided to enable a fluid, such as a gas or liquid to
be injected into the tube causing the tube to expand. The tube also
includes flexible, but inextensible fibers or other material that
prevents the tube from expanding along the axis. Typically, the fibers
are fastened at each end of the tube. As a result, when air is injected
into the inlet, the tube expands radially, in a direction transverse to
the axis and contracts in length along the axis. When the air is
released, the tube contracts radially and extends axially. In this way,
the actuator can be used to cause a device, such as a robotic arm to
move.

[0009] One of the drawbacks of these pneumatic actuators is that they can
be difficult to control with respect to position (contraction length) and
force (contraction force) due to their inherent nonlinear behavior.
Extrinsic sensors, for example, located on the joint or elsewhere on the
device, external to the actuator can be used. However, these extrinsic
sensors make the system bulky, heavy, and complex, outweighing any
potential advantages of using relatively small and light weight
pneumatics for actuation.

SUMMARY

[0010] The present invention is directed to mechanical actuators that
include embedded sensors that enable control of the actuator in
real-time. The actuators can include pneumatic actuators that contract
along a working axis in response to fluid being injected into a chamber
or cavity that can expand in a dimension transverse to the axis. The
actuators can include restraining elements, such as flexible but
inextensible fibers, such as cables or Kevlar fibers, that react to the
expanding cavity to contract the actuator along the axis. These actuators
can be used as artificial muscles to actuate mechanical devices, such as
robotics and prosthetics.

[0011] In accordance with various embodiments of the invention, the
pneumatic artificial muscle actuator can be provided with integrated
sensing capabilities inspired by--muscle spindles and Golgi tendon
organs--receptor organs that provide the means for elegant control loops
in biological systems. In accordance with the invention, the integrated
sensors can measure the change in length and the change in tension force
of the PAM actuator.

[0012] In accordance with one embodiment of the invention, the pneumatic
actuator can be formed from an elastic material that includes a chamber
extending along an axis from a first end to a second end. The actuator
can include an inlet connected to the chamber to enable a fluid to be
injected into the chamber. The actuator can include a plurality of
flexible fibers coupled to the first end and the second end that prevent
the actuator for extending along the axis. The actuator can also include
a first sensor layer positioned along the actuator between the first end
and the second end and coupled to the actuator, whereby when a fluid is
injected into the chamber causing the chamber to expand, the first sensor
layer is caused to expand and wherein the first sensor layer includes a
first microchannel containing a conductive liquid extending along a
portion of the actuator whereby expansion of the first sensor layer
causes a change in at least one dimension of the microchannel and a
change in electrical resistance of the conductive liquid in the first
microchannel.

[0013] These and other capabilities of the invention, along with the
invention itself, will be more fully understood after a review of the
following figures, detailed description, and claims.

BRIEF DESCRIPTION OF THE FIGURES

[0014] FIG. 1A is a diagram of an embodiment of a pneumatic actuator in
the unactuated/relaxed position according to the invention.

[0015] FIG. 1B is a diagram of an embodiment of a pneumatic actuator in
the actuated position according to the invention.

[0016] FIG. 2 is a diagram showing the layers an embodiment of a pneumatic
actuator according to the invention.

[0017] FIG. 3A is a diagram of a cross-section of an embodiment of a
pneumatic actuator in the unactuated/relaxed position according to the
invention.

[0018] FIG. 3B is a diagram of a cross-section of an embodiment of a
pneumatic actuator in the actuated position according to the invention.

[0019] FIG. 4 is a diagram of a method for making an embodiment of a
pneumatic actuator according to the invention. FIG. 4 shows the
fabrication process for embedding a helical microchannel in an elastomer
tube. The elements of the process can include (a) Prepare outer and inner
molds; (b) Pour liquid elastomer, and when the elastomer cures; (c)
Remove the outer mold; (d) Wrap the cured elastomer tube with a thin and
low-friction fiber in a helical shape; (e) Prepare the second outer mold.
(f) Pour liquid elastomer. (g) Remove outer and inner molds when the
second poured elastomer cures. (h) Pull the low-friction fiber out from
one end making the helical trace (microchannel) in the elastomer tube.

[0020] FIG. 5 is a diagram of showing an embodiment of a pneumatic
actuator at various stages in the fabrication process according to the
invention.

[0021] FIG. 6A is a diagram of an alternative embodiment of a pneumatic
actuator according to the invention.

[0022] FIG. 6B is a diagram showing the layers an alternative embodiment
of a pneumatic actuator according to the invention.

[0023] FIG. 7A is a diagram of a cross-section of an alternative
embodiment of a pneumatic actuator in the unactuated/relaxed position
according to the invention.

[0024] FIG. 7B is a diagram of a cross-section of an alternative
embodiment of a pneumatic actuator in the actuated position according to
the invention.

[0025] FIG. 8 is a diagram of a method for making an alternative
embodiment of a pneumatic actuator according to the invention.

[0026] FIG. 9 is a diagram of a method for making an alternative
embodiment of a pneumatic actuator according to the invention.

[0027] FIG. 10 is a diagram of showing an alternative embodiment of a
pneumatic actuator at various stages in the fabrication process according
to the invention.

[0028] FIGS. 11(a) and 11(b) show a sensor integrated into a single unit
actuator. FIG. 11(a) shows a front side showing the first sensor layer
(layer 3a in FIG. 6) above the Kevlar fibers; and FIG. 11(b) shows the
back side showing the second sensor layer (layer 1b in FIG. 6) below the
Kevlar fibers.

[0029] FIGS. 12(a), 12(b) and 12(c) show a multi-cell pneumatic actuator
according to the invention with multiple embedded zero-volume air
chambers. FIG. 12(a) shows a prototype; FIG. 12 (b) shows a relaxed
actuator; and FIG. 12(c) shows a contracted actuator.

[0030] FIGS. 13(a) and 13(b) show an example of a characterization system
for a multi-cell actuator according to the invention. FIG. 13(a) shows
the characterization setup; and FIG. 13(b) shows the characterization
result showing force and contraction length responses with different air
pressure.

[0031] FIGS. 14A, 14B and 14C show an alternative method of making a
pneumatic actuator according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] The present invention is directed to an actuator that includes
integrated sensing and can provide real-time reporting of position and
force to provide real-time control of the actuator. The actuator can be
provided in different embodiments according to the application.

[0033] FIGS. 1A and 1B show one embodiment of an integrated actuator 100
according to the invention. FIG. 1A shows the integrated actuator 100 in
a relaxed or unpressurized state. FIG. 1B shows the integrated actuator
100 in a contracted or pressurized state. In accordance with some
embodiments of the invention, the actuator 100 can include an actuator
body 110 that extends between a first end 102 and a second end 104, an
includes an inlet 120 to enable a fluid, such as a gas or liquid to be
injected into the central cavity or chamber inside the actuator 100.

[0034] In accordance with some embodiments of the invention, the actuator
body 110 can be formed by one or more layers of an elastomer material
that can expand when a fluid is injected into the cavity of the actuator
100 and then return to the relaxed or unpressurized state when the fluid
is released and allowed to escape the cavity. In some embodiments, the
elastomer material can include a high elasticity silicone rubber such as
Dragon Skin from Smooth-on, Inc., Easton, Pa. The elastomer material can
be selected from a wide range of elastomer materials, including rubber,
silicon, polyurethane and PDMS.

[0035] In operation, the actuator 100 can extend and contract along an
axis that extends between the first end 102 and the second end 104. The
first end 102 and second end 104 can include any known fastening element
to allow the ends to be attached to a device to be actuated. The ends 102
and 104 can, for example, include loops to allow them to be bolted to an
actuated device or include threaded posts that enable them to be
connected to a threaded hole or by use of a mating nut or other
internally threaded element.

[0036] In accordance with some embodiments of the present invention, the
actuator body can include a restraining component that is adapted to
cause the actuator to contract along an axis in response to an expansion
force applied transverse to the axis. The restraining component, for
example, can be constructed from fibers, cords, cables, sheets or
mechanical linkages or a combination of mechanical linkages and fibers,
cords, cables or sheets.

[0037] In accordance with some embodiments of the invention, the actuator
body 110 can include a restraining component that includes one or more
flexible, but inextensible fibers 124 that are positioned along or
parallel to the axis that extends between the first end 102 and the
second end 104. One or more of the fibers 124 can be connected, directly
or indirectly to each of the ends 102 and 104. The fiber 124 can be used
to prevent the actuator 100 from extending in length when fluid is
injected into the cavity or chamber. However, the fibers 124 enable the
actuator 100 to expand radially, transverse to the axis that extends
between the ends, causing the actuator to contract axially pulling the
ends 102 and 104 together. The fibers 124 can be embedded into the
flexible material that forms the actuator body 110 or be positioned
outside of at least one layer of material that forms the actuator body
110. In accordance with some embodiments of the invention, the fibers can
be Kevlar TM fibers, cord or cables, metal cables (e.g., steel cable), or
other flexible, but substantially inextensible materials. In addition to
cables or fibers, the fiber materials can be woven into a fabric or sheet
configuration.

[0038] A fluid control system can be provided to control the flow of fluid
into the actuator 100. The inlet 120 can be provided in the form of an
inlet tube 120 or connection for connecting a hose or other conduit that
enables the fluid to be injected into the cavity inside the actuator 100.
A valve or other fluid flow control element can be coupled to the inlet
to control the flow of fluid into and out of the actuator 100. In
accordance with some embodiments, the fluid can be a gas, such as, air or
a liquid, such as water or hydraulic fluids. Other gases, such as inert
gases, or liquids can be used depending on the environment.

[0039] In operation, a fluid under pressure can be allowed to flow into
the central cavity or chamber of the actuator body 110 causing it to
expand radially, transverse to the axis of the body 110. The expansion
causes the fibers to expand radially as well, shortening the distance
between the ends of the fibers, causing the body 110 to contract in
length along the axis as shown in FIG. 1B. When the fluid is released or
allowed to escape the central cavity or chamber of the actuator body 110,
it extends along the axis and returns to its initial state as shown in
FIG. 1A. In accordance with the invention, the fluid can be any gas or
liquid, including, for example, air and water. The fluid selected for a
given application can be selected as a function of on the environment and
forces required.

[0040] In accordance with some embodiments of the invention, the actuator
body 110 can include one or more sensing elements integrated into the
actuator body material. The sensing elements can be components that can
be used to report a change in a physical dimension of the actuator body
110.

[0041] In accordance with some embodiments of the invention, the sensing
elements can include one or more microchannels 130 embedded in the
actuator body 110 that includes a conducting liquid that changes
electrical resistance when the actuator body 110 expands. Wires can be
connected to the ends of the microchannels 130 to measure the change in
resistance as the actuator body 110 contracts and extends. In accordance
with some embodiments, the microchannel 130 can be formed in a spiral or
helix that extends around at least a portion of the actuator body 110 and
axially along at least a portion of the actuator body 110. In accordance
with some embodiments, more than one microchannel 130 can be provided and
the microchannels can be provided in any of the layers of the actuator
body 110.

[0042] FIG. 2 is a diagram depicting the layers that can be provided in an
actuator 100 according to some embodiments of the invention. In these
embodiments, the actuator body 110 can be constructed from 3 or more
layers of flexible material. The inner most layer, layer 1 212 can
enclose the air chamber 222 that can be connected to inlet 120. Layer 1
212 can be formed from an elastomer and include one or more
microchannels, such as microchannel 232 formed in a helix or spiral
around the air chamber 222. In accordance with some embodiments, the
microchannel 232 can be filled with a non-toxic conducting liquid, e.g.
eutectic Gallium-Indium (eGaIn) or eutectic Gallium-Indium-Tin
(Galinstan). The second or middle layer, layer 2 214, can include
flexible, but inextensible fiber 224 that extend parallel to the axis of
the actuator and can be fixed at both ends 102, 104 of the actuator body
110. The fibers 224 can be embedded in a flexible material as shown or
can simply be positioned between the inner layer, layer 1 212 and the
outer layer, layer 3 216. The outer layer, layer 3 216 can be formed from
an elastomer and include one or more microchannels, such as microchannel
234 formed in a helix or spiral around layer 2 214 or the fibers 224. As
with microchannel 232, the microchannel 234 can also be filled with a
non-toxic toxic conducting liquid, e.g. eutectic Gallium-Indium (eGaIn)
or eutectic Gallium-Indium-Tin (Galinstan). Wires, not shown, can be
connected to each end of the microchannel and in electrical contact with
the conducting liquid to enable a control system to measure a change in
the electrical resistance of the conducting liquid as the actuator
expands and relaxes.

[0043] In operation, when the actuator contracts, microchannel 232 and
microchannel 234 containing liquid metal in the both inner (layer 1 212)
and outer layer (layers 3 216) are stretched, as shown in FIG. 3B, and
the electrical resistance of the liquid conductor increases. This
resistance change can be used to determine the axial displacement of the
actuator (actuator contraction) by empirically determining the resistance
at two or more displacements and estimating or extrapolating intervening
positions.

[0044] The operation of the pneumatic actuator 100, 200 can be better
understood by evaluating the differential effect of compressed air (or
fluid) on the behavior of the inner microchannel 332 and outer
microchannel 334. When the two ends of the actuator are fixed, as
compressed air enters the air chamber, the overall geometry of the muscle
remains almost the same, but the pressure of the air chamber increases.
The result is that the inner layer (Layer 1 312) is pushed out by the
internal air pressure, but at the same time is compressed by the fibers
324. The fibers 324 cover only certain areas of the inner microchannel
332. Those areas of the inner microchannel 332 that are covered by (e.g.
intersect) the fibers 324 are compressed and deformed, compare FIG. 3A
with FIG. 3B. The overall effect is an increase in electrical resistance
of the inner microchannel 332 of the inner layer (Layer 1 312). However,
the electrical resistance change of the outer microchannel 334 is little
because this microchannel is neither elongated nor compressed. If the
load on the muscle is very low impedance, the resistance increases in the
two microchannels are almost the same, but if the load is higher
impedance then the two microchannels give different responses with a
larger resistance increase in the inner microchannel. Therefore, using
these two microchannels, the system can determine the contraction length,
the load and the contraction force at the same time.

[0045] In accordance with some embodiments of the invention, the outer
microchannel 334 can be used for measuring the change in length of the
actuator 100, and the inner microchannel 332 can be used for measuring
the change in contraction force of the actuator 100. If the length and
force change happen simultaneously, the sensor signal of the outer
microchannel 334 can be subtracted from that of the inner microchannel
332 to measure contraction force because the inner microchannel is
experiencing both elongation and compression at the same time.

[0046] In accordance with some embodiments of the invention, the force and
displacement of the actuator 100 can determined empirically by placing
the actuator 100 in a fixture that measures the contraction force as air
pressure is applied to the actuator 100. By fixing the second end 104 and
attaching the first end 102 to a scale, such as a spring scale, the force
and length of the actuator can be measured as different amounts of
pressure is applied. Using 2 or more data points, the force and
displacement can be determined from the empirical data.

[0047] FIG. 4 illustrates one example of the fabrication process for
making helical microchannels embedded in an elastomer actuator body 110,
according to some embodiments of the invention. The number of turns in
the helix can be used to select the sensitivity, with the more turns
providing higher sensitivity. In accordance with this embodiment of the
invention, the channel can be formed within the elastomer by keeping a
wrapped low-friction fiber having a diameter or cross-sectional dimension
of 125 micrometers (e.g., Dyneema or Spectra) in place when the elastomer
is in its liquid state, and then removing the fiber when the elastomer is
cured. In other embodiments, the low-friction fiber can have a diameter
or cross-sectional dimension of in the range from 50 to 1000 micrometers

[0048] In accordance with some embodiments of the invention, the
microchannels can be formed having a cross-section dimension in a range
from 50 micrometers to 1000 micrometers. The dimensions of the
microchannels 332 and 334 can be determined based on the application,
including the amount of force to be applied and dimensions of the
actuator itself. In accordance with one embodiment of the invention, a
pattern that can be used as a guide for the location of the low-friction
fiber can be made in the outer mold shown in FIG. 4 to make the location
of the microchannel more consistent. The mold can include an inner post
and an outer mold as shown in step 4(a). The elastomer material, in
liquid form, can be poured or injected into the mold and allowed to cure
as shown in step 4(b). The cured elastomer layer can be removed from the
mold as shown in FIG. 4(c). The helical microchannel pattern in the outer
mold provides the location on the cured inner tube for insertion of a
filler element or material, such as, a low-friction fiber or cord (e.g.,
Dyneema, available from DSM Dyneema LLC, Stanley, NC or Spectra,
available from Honeywell International, Colonial Heights, Va.), as shown
in step 4(d). The cured inner tube with the low-friction fiber is
inserted into a larger outer mold at step 4(e) and an outer layer of
elastomer is applied at step 4(f). After the outer layer is cured, the
completed layer is removed from the outer mold (and the inner post is
removed) at 4(g). The low-friction fiber can be removed from the
completed layer at step 4(h), leaving the complete layer with a
microchannel to be filled with a conductive liquid. The mold components
can be formed, for example, using a 3-D printer.

[0049] Examples of an elastomer tube with embedded helical microchannels
are shown in FIGS. 5(a)-5(d). FIG. 5(a) shows, according to one
embodiment of the invention, an elastomer tube in a 3D printed mold with
embedded Dyneema and Kevlar fibers. FIG. 5(b) shows the elastomer tube
after removing Dyneema fibers. FIG. 5(c) shows the elastomer tube after
removing the elastomer tube from the 3-D printed mold. FIG. 5(d) shows an
example of an actuator according to an embodiment of the invention having
a pneumatic fitting, eGaIn conducting liquid injected in the helical
microchannel and wires connected to the eGaIn conducting liquid.

[0050] The sensing actuator according to the invention can also be used to
mimic the function of natural muscles, without being limited by its
cylindrical form. This embodiment of the invention can be used in
applications in which the muscle mimic can be embedded in material that
surrounds a portion of the body, for example, in active physical therapy
and active prosthetic applications. In accordance with the invention, the
sensing actuator can be formed, similar to a biological muscle, in a
substantially two-dimensional or flat configuration. The flat
configuration remains substantially flat when in its relaxed state
providing a highly compact actuator that adds little additional volume so
that it can be incorporated in a brace or a suit worn on the body.

[0051] FIGS. 6A and 6B show a pneumatic actuator 600 according to an
alternative embodiment of the invention. This embodiment is similar to
the structure of the actuator shown in FIG. 1, except that it has a
two-dimensional flat configuration with multiple stacked layers that
make-up the actuator body 610. Like the actuator shown in FIGS. 1A and
1B, the actuator body 610 extends along an axis from a first end 602 to a
second end 604. The ends 602 and 604 can include fastening or attachment
elements (not shown) that enable the ends to be securely fastened to a
device to be actuated.

[0052] In accordance with some embodiments, the actuator body 610 can
include one or more layers of one or more flexible, but inextensible
fibers 624 that are positioned along or parallel to the axis that extends
between the first end 602 and the second end 604. One or more of the
fibers 624 can be connected, directly or indirectly to each of the ends
602 and 604. The fibers 624 can be used to prevent the actuator 600 from
extending in length when fluid is injected into the cavity or chamber.
However, the fibers 624 enable the actuator 600 to expand radially,
transverse to the axis that extends between the ends 602 and 604, causing
the actuator to contract axially pulling the ends 602 and 604 together.
The fibers 624 can be embedded into one or more of the layers of flexible
material that forms the actuator body 610 or be positioned outside of at
least one layer of material that forms the chamber, layer 0 611 of the
actuator body 610. As shown in FIG. 6B, the fibers 624 can, for example,
be embedded into layer 2a 615 and layer 2b 614 of the actuator body 610.
Alternatively, the material that forms layer 2a 615 and layer 2b 614 can
be omitted and the fibers 624 can be bonded in-place when layer 3a 617 is
bonded to layer 1a 613 and when layer 3b 616 is bonded to layer 1b 612.

[0053] A fluid control system can be provided to control the flow of fluid
into the actuator 600. The inlet 620 can be provided in the form of an
inlet tube or connection 620 for connecting a hose or other conduit that
enables the fluid to be injected into the cavity or chamber inside the
actuator 600. A valve or other fluid flow control element can be coupled
to the inlet 620 to control the flow of fluid into and out of the
actuator 100.

[0054] FIG. 6B shows an exploded view of the pneumatic actuator 600
according to an alternative embodiment of the invention. The inner most
layers is layer 0 611 which includes a zero-volume fluid chamber in the
middle of the layer. Layer 0 611 can be formed from two flat sheets of
material that are bonded together with a specific area in the middle that
prevents the two layers from being bonded during the fabrication. Like a
bladder that has been pressed flat, this middle area has no volume when
it is not inflated. However, it inflates when a fluid, such as,
compressed air, is injected inside, and the fixed length of the fibers
makes the muscle contract in the axial direction of the fibers, as shown
in FIGS. 7A and 7B. The zero-volume fluid chamber enables the actuator to
be compact in its relaxed state. It is not necessary that the fluid
chamber in layer 0 be zero volume.

[0055] In accordance with some embodiments of the invention, the actuator
body 610 can include layers above and below layer 0 611 that includes the
fluid chamber. As shown in FIG. 6B, the actuator body 610 can include
layer 1a 613, layer 2a 615 and layer 3a 617 above layer 0 and layer 1b
612, layer 2b 614 and layer 3b 616 below layer 0. In accordance with some
embodiments of the invention, some of these layers can be omitted
depending upon the application of the actuator.

[0056] In accordance with some embodiments of the invention, one or more
of the layers of the pneumatic actuator 600 can include microchannels 630
that contain a conductive liquid that changes electrical resistance as
the layer stretches to enable position and force sensing. The
microchannel 630 embedded eGaIn or Galinstan sensing layers, inner (layer
1b 612) and outer (layer 3a 617) of the actuator 600 can detect both the
contraction length and force changes of the muscle in the same way as
described for the embodiment of FIGS. 1A, 1B and 2. In accordance with
some embodiments of the invention, the microchannels 630 are formed in a
flat material according to a pattern that results in a change in one or
more physical dimensions of the microchannel when the layer is stretched
as fluid is injected into the fluid chamber. FIGS. 6A and 6B show that
the microchannel forms a "zig-zag" pattern that can extend from proximate
the first end 602 to proximate the second end 604, but traverses back and
forth across the surface, transverse to the axis of the actuator 600.

[0057] FIGS. 7A and 7B show a cross-section of the actuator 600 of FIG. 6
in the relaxed state and the expanded state, respectively. As shown in
FIG. 7A, the actuator 700 can be substantially flat with each layer,
extending substantially parallel to the next. As shown in FIG. 7B, when
the fluid chamber is inflated, each of the layers expands transverse to
the axis of the actuator body 610 and causing the fibers 724 in layer
2b614 to bear against the microchannels 630 in layer 1b 612, changing the
electrical resistance differently than that of microchannels 630 in layer
3a 617. This enables the microchannels 630 in layer 1b 612 to be used to
measure the change in the contracting force and the microchannels 630 in
layer 3a 617 to be used to measure the change in the length of the
actuator. Where the length and force change happen simultaneously, the
sensor signal of the outer layer, layer 3a 617 can be subtracted from
that of the inner layer, layer 1b 612 to measure contraction force
because the microchannel in inner layer, layer 1b 612 is experiencing
both elongation and compression at the same time.

[0058] One example of the fabrication process for making a zero-volume
fluid chamber is shown in FIG. 8. The fabrication process, shown in FIG.
8, to make a zero-volume air chamber includes: (a) Prepare the bottom
mold; (b) Pour the liquid elastomer and allow it to cure; (c) Position
the negative mask on the cured elastomer. (d) Spray the pattern release
material. A pattern release material is sprayed on the unmasked area to
prevent the bottom layer from becoming bonded to the top layer. (e)
Remove the mask; (f) Place the second top mold on the bottom mold; (g)
Pour the liquid elastomer; and (h) Remove top and bottom mold when the
elastomer cures. The release material will prevent the top layer from
adhering to the bottom layer in area of the chamber. An inlet can either
be fabricated into the layer, e.g., using the release material, providing
an inlet tube or cutting, drilling or boring into the chamber. A cleaning
fluid can be introduced into the chamber to remove the release material,
if necessary.

[0059] An alternative fabrication method is shown in FIG. 9. Instead of
using pattern release spray, a positive mask prevents the liquid
elastomer from being coated. The alternative fabrication process of FIG.
9 to make a zero-volume fluid chamber includes: (a) Prepare the bottom
mold. (b) Pour the liquid elastomer and allow it to cure. (c) Place the
positive mask. (d) Spin coat a layer of liquid elastomer. (e) Remove
mask. (f) Partial bake. (g) Laminate a cured top layer onto the bottom
layer. (f) Remove mold when the elastomer layer cures. While the method
of FIG. 8 repeats pouring processes, the method of FIG. 9 requires a
bonding process of two cured layers. These fabrication methods for
zero-volume air chambers can be also used for making zero-volume
microchannels for sensing as an alternative to the molding and casting
process.

EXAMPLES

[0060] One example of an actuator according to the invention and its
intermediate fabrication stages are shown in FIGS. 10(a) and 10(b). FIG.
10(a) shows the front and back sides of the completed device. FIG. 10(b)
shows the fibers and a sensor layer bonded in 3D printed mold. Detailed
views of one completed prototype according to the invention are shown in
FIGS. 11(a) and 11(b). FIG. 11(a) shows front side with the sensor layer
over the fiber layer. FIG. 11(b) shows the back side with the fiber layer
over the sensor layer. The actuator shown in FIGS. 10(a), 10(b) and
11(a), 11(b) has a single unit zero-volume air chamber and embedded
microchannels in multiple flat layers. By connecting or fabricating the
actuators in series along their axis, a group of multiple flat actuators
can be made, as shown in FIG. 12. The example shown in FIG. 12 has the
capability of more than 25% contraction. While a serial configuration of
multiple muscles increases the contraction length, a parallel
configuration may be used to increase the contraction force.

[0061] FIGS. 13(a) and 13(b) show an example of a characterization system
and an example of a resulting characterization of a multi-cell actuator
according to one embodiment of the invention. As shown in FIG. 13(a), the
characterization system can include a commercial material stress/strain
tester and the multi-cell actuator can be tested by injecting compressed
air into the actuator at predefined pressures (e.g., 5, 7.5, 10, 12.5 and
15 psi).

[0062] The contraction force and length can be measured for different air
pressures using a commercial materials tester. FIG. 13(b) shows the
characterization result including the force and contraction curves for
each air pressure value.

[0063] FIGS. 14A, 14B and 14C show a diagram of an alternative method for
forming the helical microchannels 1330 in the elastomer material
according to some embodiments of the invention. In this method, the
helical channel can be produced in a substantially straight and flat
layer as shown in FIG. 13A. The microchannel can be formed by molding a
base layer with a microchannel and then bonding a layer over it or by
molding the layer using a low-friction fiber, such as the Dyneema, or
Spectra fiber identified above. After the microchannel layer has cured,
it can be wrapped in a helical or other fashion around an inner mold and
inserted into an outer mold as shown in FIG. 14B. The inextensible fibers
1324 can be held in place in the mold as liquid elastomer is poured or
injected into the mold cavity forming a layer that includes both
microchannels 1330 and inextensible fiber 1324. After curing, shown in
FIG. 14C, the resulting tubular component can be removed from the mold
and used to construct a pneumatic actuator according to the invention. An
outer layer providing a second microchannel 1330 can be added to
resulting tubular component shown FIG. 13C, by wrapping a second
microchannel layer around the tubular component and pouring or injecting
liquid elastomer to form an outer layer similar to the method shown in
FIG. 14B.

[0064] Other embodiments are within the scope and spirit of the invention.
Further, while the description above refers to the invention, the
description may include more than one invention.